A photoreaction means the general chemical reaction that causes molecules (i.e., radical reactant) to absorb energy by light irradiation, to be excited to the state of the higher energy level (i.e., excited state) and thereby to induce the reaction. The photoreaction is also called a photochemical reaction. According to “Kagaku Jiten” p 457-458, Tokyo Kagaku Dojin, photoreactions include oxidation-reduction reactions by light and substitution and addition reactions by light. As is known, a photoreaction is applicable to not only photographic industries, photocopying technology, induction of photovoltaic power, but syntheses of organic compounds. Photochemical smog is also the unintentional photochemical reaction.
As described in JP 2010-6775A or Journal of the Japan Petroleum Institute, Vol. 17, No. 10 (1974) p 72-76, there is a known technique of synthesizing cyclohexanone oxime by a photochemical reaction. It is also known that the wavelength of 400 to 760 nm is desirable as the effective wavelength for the reactions of a cycloalkanone oxime. Examples of the light emitter having the energy output characteristics specialized in such specific wavelength range include light sources such as light emitting diodes, lasers and organic electroluminescence (organic EL).
Light emitting diodes have the advantage of directly converting electrical energy into light with a semiconductor. The light emitting diodes attract attention because of less heat generation, efficient use of energy and long life. With recent development of LEDs of high efficiency and high output, LEDs can replace incandescent lamps and fluorescent lamps in general lighting purposes. As for industrial purposes, LEDs are expected to reach the practical level in several years.
In such an environment, the method of producing a cycloalkanone oxime proposed in JP 2010-6775A has the following characteristics: (i) It is preferable that in the emission energy distribution with respect to the wavelength of the light source, the emission energy in the wavelength range of less than the wavelength of 400 nm is equal to or less than 5% of the maximum value of emission energy and the emission energy in the wavelength range of greater than the wavelength of 760 nm is equal to or less than 5% of the maximum value of emission energy. (ii) The light emitting diodes have an energy conversion efficiency equal to or greater than 3%. (iii) A plurality of light emitting diodes arrayed in a plane along the side face of a photochemical reactor containing a photoreaction liquid are used to irradiate the photochemical liquid with light via a permeable photochemical reactor.
According to the technique described in JP 2010-6776A, cyclohexanone oxime is synthesized under the following conditions. Light emitting diodes are used as the light source. In the emission energy distribution with respect to the wavelength of the light source, the wavelength at which emission energy has a maximum value is 400 nm to 760 nm. A cooling jacket is provided on the rear face of the light source to continuously introduce a coolant to the cooling jacket and forcibly and indirectly cool down the light source. In the emission energy distribution with respect to the wavelength of the light source, the wavelength at which emission energy has a maximum value is 430 nm to 650 nm. The integrated value of emission energy at the wavelengths of 400 nm to 760 nm relative to the emission energy in the wavelength range of 300 nm to 830 nm is equal to or greater than 95%. JP 2010-6776A additionally includes descriptions on the temperature of the coolant introduced into the cooling jacket, the method of arranging the light emitting diodes, and the minimum distance of irradiation between the light emitting diodes and the side face of the photochemical reactor. JP 2011-521004A describes photonitrosation of a cycloalkanone oxime conducted in a very small space with a microreactor using light emitting diodes.
The amount of the cycloalkanone oxime produced per unit electric power by the method described in any of the publications above is, however, not sufficiently high compared to the industrially practical level. There is thus a requirement for further improvement of the utilization efficiency of energy.
It could therefore be helpful to provide a production method that produces a cycloalkanone oxime at a high yield by photonitrosation using a light source having a narrow wavelength distribution and thereby enables power saving and resource saving in production of the cycloalkanone oxime.